A known seat occupancy determination device is disclosed in JP2011-17592A (hereinafter, referred to as Patent reference 1). According to Patent reference 1, a load sensor is placed between a cushion portion of a vehicle seat and a floor of the vehicle. The seat occupancy determination device disclosed in Patent reference 1 determines a seat occupancy state of the vehicle seat by comparing a total sum of load value detected by the load sensors with a predetermined load threshold value. The known seat occupancy determination device disclosed in Patent reference 1 is provided with the right-left pair of load sensors which are provided only at a rear portion of the cushion portion due to cost reduction measures. Thus, the accuracy of the load value detected by each of the load sensors may vary because the load applied to the cushion portion is unbalanced either in a front direction or a rear direction due to an inclination or a tilt of the vehicle in the front-rear direction
Dealing with this inaccuracy of the load value detected by the load sensors, the known seat determination device disclosed in Patent reference 1 determines an inclination state or a tilt state of the vehicle and corrects the load value detected by the load sensors in response to the determined inclination state. In particular, in a state where the vehicle seat is not occupied, that is, the vehicle seat is neither seated by, for example, an adult, an infant or a child, nor fixed with a child safety seat, the determination of the inclination state of the vehicle in the front direction is performed at three levels based on a tensile load value detected by the load sensors. Then, when the vehicle seat is seated by, for example, an adult, an infant or a child, the seat occupancy determination device corrects the total sum of the load value detected by the load sensors to increase in accordance with an immediately preceding determination result of the inclination and compares the corrected load value with the load threshold value. Based on the compared result, whether the vehicle seat is seated by an adult, an infant or a child, or whether a child safety seat is fixed to the vehicle seat is determined.
As described above, the known seat occupancy determination device disclosed in Patent reference 1 corrects a detected load value in response to the determination result of the inclination, or the tilt of the vehicle. Accordingly, the variation of the load value detected by the load sensors may be reduced in a state where the vehicle is inclined or tilted.
The pair of load sensors of the known seat occupancy determination device may be mounted to a front portion and a rear portion of one of a left portion and a right portion of the vehicle seat. When mounting the pair of load sensors to only one of the right portion and the left portion of the vehicle seat, the detection accuracy is enhanced in a case where the pair of load sensors is mounted to a center side of the vehicle. The center side of the vehicle corresponds to the left portion of a passenger seat of a vehicle with left-hand steering wheel when facing a front of the vehicle while corresponding to the right portion of the passenger seat of a vehicle with right-hand steering wheel.
FIG. 8 shows a relationship between an inclination angle, or a tilt angle of the vehicle in a right-left direction and the detected load value in a case where the front-rear pair of load sensor and the load sensor is mounted to the left portion of the passenger seat of the vehicle with left-hand steering wheel instead of mounting the pair of load sensors to a right portion and a left portion of the rear of the vehicle seat. A lateral axis shows the inclination angle, or the tilt angle in the vehicle right-left direction, and a longitudinal axis shows the total sum of the load value detected by the pair of load sensors in each of the seat occupancy state. A dashed straight line NV shown in FIG. 8 divides a determination range whether an adult passenger is seated in the vehicle seat or whether a child safety seat (indicated as CRS in FIG. 8) is fixed to the vehicle seat. A hatching portion corresponds to a threshold value range formed as a predetermined range including the straight line NV to stabilize the determination accuracy. In a case where the total sum of the detected load value is above the threshold value range, it is determined that the vehicle seat is seated by an adult passenger. In a case where the total sum of the detected load value is below the threshold value range, it is determined that a child safety seat is fixed to the vehicle seat 1. In a case where the total sum of the detected load value is somewhere in the threshold value range, the seat occupancy state of the vehicle seat is assumed to be indeterminate, leading to deteriorate the reliability of the determination result.
As shown in FIG. 8, in a case where the vehicle is inclined or tilted in the right direction when the vehicle seat is seated by an adult passenger, the total sum of the detected load value is reduced and enters into or goes below the threshold value range. Accordingly, the determination of the seat occupancy state of the vehicle seat cannot be performed or can be wrongly performed that a child safety seat is fixed to the vehicle seat. On the other hand, in a case where the vehicle is inclined or tilted in the left direction when a child safety seat is fixed to the vehicle seat, the total sum of the detected load value increases and enters into the threshold value range. In those cases, the determination of the seat occupancy state may not be performed.
On the other hand, FIG. 9 shows a relationship between the inclination angle or the tilt angle and the detected load value in a case where data processing is operated based on a method which is for enabling to determine the seat occupancy state regardless of the inclination or the tilt of the vehicle in the right-left direction. According to the method, in a case where the vehicle seat is seated by an adult passenger, the total sum of the detected load value is corrected to increase in response to the inclination angle as long as the vehicle is inclined or tilted in the right direction. In a case where a child safety seat is fixed to the vehicle seat, the total sum of the detected load value is corrected to decrease in response to the inclination angle as long as the vehicle is inclined or tilted in the left direction. As shown in FIG. 9, by correcting the total sum of the detected load value to increase or to decrease, the total sum of the load value comes out of the threshold value range so that the determination of the seat occupancy state in each case can be performed.
However, the determination of the seat occupancy state in each case cannot be performed or can be wrongly performed even though the total sum of the detected load value is corrected. That is, in a case where the inclination angle or the tilt angle of the vehicle is extremely increased, the correction amount has to be equivalently great in order to prevent the total sum of the load value from entering into the threshold value range. However, in a case where, for example, the determination of three or more types of seat occupancy states which include plural threshold value ranges is performed instead of two types of seat occupancy states as shown in FIG. 8, the determination of the seat occupancy state may not be performed precisely because the total sum of the load value may enter into wrong threshold value range in a case where the correction amount is set to be excessively high.
A need thus exists for a seat occupancy determination device and a seat occupancy determination method which are not susceptible to the drawback mentioned above.